1. Field of Invention
The invention relates to an automatic transmission, and more particularly to a hydraulic pressure control apparatus for controlling engagement elements accommodated in a planetary gear transmission mechanism of the automatic transmission.
2. Description of Related Art
Hitherto, an automatic transmission incorporates a planetary gear transmission mechanism for realizing a predetermined gear ratio by using selective engagement of friction members constituting a plurality of engagement elements, such as clutches and brakes; and a hydraulic pressure control apparatus for controlling a hydraulic pressure servo for engaging/releasing the frictional members of each engagement element of the transmission mechanism. The conventional circuit structure of the foregoing hydraulic-pressure control apparatus having a relatively small number of gear ratios is such that shift valves which are switched among the gear ratios are provided to correspond to the number of the gear ratios. Moreover, hydraulic pressure sequentially passes through the shift valves so as to be applied to a predetermined hydraulic pressure servo.
To meet requirements including a requirement for reducing fuel consumption, the number of the gear ratios of the automatic transmission has been increased. As a technique for increasing the number of gear ratios by combining a plurality of planetary gears, a technique has been disclosed in Japanese Patent Laid-Open No. 4-219553. The technique is to use a gear train constituted by combining a planetary gear for inputting reduced speed with a Ravigneaux-type planetary gear set. Thus, a small number of transmission elements and of engagement elements are able to realize six speeds in the forward direction and one speed in the reverse direction.
When the planetary gear transmission mechanism having the multiple gear ratios is controlled by a conventional circuit structure having shift valves, the number of valves undesirably increases. Thus, the cost is enlarged excessively. Moreover, the circuit structure becomes furthermore complicated, causing the size of the hydraulic-pressure control apparatus to be undesirably enlarged. Usually, the hydraulic-pressure control apparatus has a structure formed into a valve body which totally incorporates each of valves. The valve body is disposed in the side portion of the transmission mechanism. Therefore, when the size of the valve body is enlarged, the size of the transmission is correspondingly enlarged. As a result, easy mounting on the automatic transmission is inhibited. Therefore, simplification of the circuit structure free of shift valves is required.
The disclosed technique is such that a one-way clutch which is capable of mechanically shifting torque when the engagement element has been released is provided for only the first speed to realize a compact transmission. As a result, gear shift to the second or higher speed is realized by changing clutching of the friction engagement element by using control of the hydraulic pressure. The control of clutching must be performed with a satisfactory response of the hydraulic pressure servo such that either of the frictional engagement elements is engaged while the other frictional engagement element is released. To simplify the circuit structure and improve the controllability of each engagement element, it might be considered feasible to structure the hydraulic pressure circuit for controlling each engagement element. That is, a special control valve (a linear solenoid and a duty solenoid) is provided for each engagement element so as to be independently controlled.
Thus, shift of the gear to each gear ratio can be performed such that the frictional engagement element to be engaged and the frictional engagement element to be released can directly be controlled. Because each of the special control valves is provided, jump of shift is permitted. If breakdown of the solenoid of the control valve for controlling each engagement element occurs or a mistake of a signal is made, so-called interlocking occurs. That is, two or more frictional engagement elements, the engagement of which must be prevented, are engaged in a predetermined gear ratio. As a result, the durability of each frictional engagement element deteriorates.
Accordingly, an object of the invention is to provide a hydraulic pressure control apparatus for an automatic transmission which is capable of overcoming the foregoing problems and which has a circuit structure permitting a jump of the gear ratio and enablement to prevent the occurrence of interlocking of the transmission mechanism.
To achieve the foregoing object, according to the invention, there is provided a hydraulic pressure control apparatus for an automatic transmission including a planetary gear transmission mechanism incorporating at least five engagement elements to selectively be engaged to realize a predetermined gear ratio; and a hydraulic-pressure control apparatus for controlling the engagement elements of the transmission mechanism so that when a first engagement element C-1 and a fourth engagement element B-3 are engaged, a first speed is realized; when the first engagement element C-1 and a fifth engagement element B-1 are engaged, a second speed is realized; when the first engagement element C-1 and a third engagement element C-3 are engaged, a third speed is realized; when the first engagement element C-1 and a second engagement element C-2 are engaged, a fourth speed is realized; when the second engagement element C-2 and the third engagement element C-3 are engaged, a fifth speed is realized; and when the second engagement element C-2 and the fifth engagement element B-1 are engaged, a sixth speed is realized, wherein the hydraulic-pressure control apparatus is provided with cutoff valves 75, 76, 77, 78 for inhibiting combinations with which interlocking of the transmission mechanism occurs due to engagement of two or more engagement elements of the five engagement elements when each of the forward gear ratios including the first speed to the sixth speed has been realized.
Specifically, it is effective that the planetary gear transmission mechanism incorporates a planetary gear for inputting reduced speed and a planetary gear set for inputting reduced revolutions from the planetary gear for inputting the reduced speed, the first engagement element C-1 is a first clutch for inputting the reduced revolutions to a first transmission element S3, the second engagement element C-2 is a second clutch for inputting revolutions input from an engine to a second transmission element C2, C3, the third engagement element C-3 is a third clutch for inputting reduced revolutions to a third transmission element S2 of the planetary gear, the fourth engagement element B-3 is a first brake for fixing the second transmission element C2, C3 of the planetary gear, and the fifth engagement element B-1 is a second brake for fixing the third transmission element S2 of the planetary gear.
It is effective that the combinations with which interlocking of the transmission mechanism occurs when the forward gear ratio has been realized and which are inhibited incorporate a first pattern having combinations of two engagements and a second pattern having combinations of three engagements, the first pattern at least incorporates four combinations of engagements between the second engagement element C-2 and the fourth engagement element B-3, between the third engagement element C-3 and the fifth engagement element B-1, between the third engagement element C-3 and the fourth engagement element B-3 and between the fourth engagement element B-3 and the fifth engagement element B-1, the second pattern incorporates two combinations of engagements among the first engagement element C-1, the second engagement element C-2 and the third engagement element C-3 and among the first engagement element C-1, the second engagement element C-2 and the fifth engagement element B-1, and the valve inhibits the above-identified six combinations.
It is effective that each of the engagement elements is provided with pressure regulating means for regulating the hydraulic pressure supplied from a hydraulic pressure source, supply/discharge of the hydraulic pressure regulated by the pressure regulating means causes engagement/release to be performed, and the valve is operated due to supply of hydraulic pressure to a predetermined engagement element.
It is effective that the third engagement element C-3 and the fourth engagement element B-3 to be engaged when the forward gear ratio has been realized are engaged so that a reverse gear ratio is realized, the combination which is inhibited when the forward gear ratio has been realized incorporates a combination of the third engagement element C-3 and the fourth engagement element B-3, and means is provided which supplies hydraulic pressure to the fourth engagement element B-3 when the reverse gear ratio has been realized.
It is effective that a first passage through which the hydraulic pressure is, through the valve 78, supplied to the fourth engagement element B-3 to be engaged when the forward gear ratio has been realized or when the reverse gear ratio has been realized and a second passage through which the hydraulic pressure is supplied without passage through the valve are provided, and the means for supplying the hydraulic pressure is the second passage.
It is effective that communication of the first passage and that of the second passage with the fourth engagement element B-3 are permitted through a switching valve, and the switch is disposed between the valve and the fourth engagement element B-3.
It is effective that the switching valve can be operated by a solenoid valve SL1 so that selective communication between the first passage or the second passage with the fourth engagement element B-3 is permitted.
It is effective that the switching valve can be operated with the hydraulic pressure which acts when the reverse gear ratio has been realized so that when the hydraulic pressure is applied, the first passage and the fourth engagement element B-3 are disconnected from one another and the second passage and the fourth engagement element B-3 are in communication with each other.
It is effective that the switching valve is a check valve, and communication of the check valve with the fourth engagement element B-3 is permitted due to the hydraulic pressure supplied through the first passage or the second passage.
It is effective that the cutoff valve is disposed between the hydraulic pressure source and the fourth engagement element B-3 to be engaged when the reverse gear ratio has been realized to cancel the communication between the hydraulic pressure source and the fourth engagement element B-3 when interlocking of the transmission mechanism has occurred, the means for supplying the hydraulic pressure is the cutoff valve, and the cutoff valve is brought to a position to permit communication between the hydraulic pressure source and the fourth engagement element B-3 due to applied hydraulic pressure which acts when the reverse gear ratio has been realized.
It is effective that the cutoff valve is structured such that the hydraulic pressure to be applied to the third engagement element C-3 is applied to the cutoff valve from at least one direction and spring force is exerted on the cutoff valve from another direction, and the cutoff valve is operated when the hydraulic pressure to be applied to the third engagement element C-3 is raised to a level higher than the spring force.
It is effective that the communication is inhibited when the forward gear ratio that has been realized incorporates a first pattern having combinations of two engagement elements and a second pattern having combinations of three engagement elements, and the cutoff valve incorporates first-pattern inhibiting (cutoff) valves 78, 77 for inhibiting the first pattern and second-pattern inhibiting (cutoff) valves 75, 76 for inhibiting the second pattern.
It is effective that the first pattern at least incorporates four combinations of engagements between the second engagement element C-2 and the fourth engagement element B-3, between the third engagement element C-3 and the fifth engagement element B-1, between the third engagement element C-3 and the fourth engagement element B-3 and between the fourth engagement element B-3 and the fifth engagement element B-1, and the first-pattern inhibiting valve incorporates a first valve 78 structured such that the hydraulic pressure is applied to at least the second engagement element C-2, the third engagement element C-3 and the fifth engagement element B-1 and the fourth engagement element B-3 is drained.
It is effective that the second pattern incorporates two combinations of engagements among the first engagement element C-1, the second engagement element C-2 and the third engagement element C-3 and among the first engagement element C-1, the second engagement element C-2 and the fifth engagement element B-1, the second-pattern inhibiting valve incorporates a second valve 75A structured such that the hydraulic pressure is applied to at least the first engagement element C-1, or the second engagement element C-2, the third engagement element C-3 and the fifth engagement element B-1 and the first engagement element C-1 or the second engagement element C-2 is drained.
It is effective that the second valve incorporates a common pressure-receiving portion to which the hydraulic pressure to be applied to the third engagement element C-3 and the fifth engagement element B-1 is applied, and a third valve 76xe2x80x2 is provided for selectively applying, to the common pressure-receiving portion, the hydraulic pressure to be applied to the third engagement element C-3 and the fifth engagement element B-1.
It is effective that the second pattern incorporates two combinations of engagements among the first engagement element C-1, the second engagement element C-2 and the third engagement element C-3 and among the first engagement element C-1, the second engagement element C-2 and the fifth engagement element B-1, and the second-pattern inhibiting valve incorporates a fourth valve 75 and a fifth valve 76 corresponding to the combinations.
It is effective that the cutoff valves 75, 76 are valves which use the hydraulic pressure to be applied to any of the engagement elements C-2, C-3; C-2, B-1 to drain the hydraulic pressure to be applied to the other engagement element C-1, the valve is structured such that the hydraulic pressure is applied to the other engagement element C-1 from one direction together with the hydraulic pressure to be applied to the engagement elements C-2, C-3; C-2, B-1 and to be operated when the hydraulic pressure to be applied to the other engagement element has been applied together with the hydraulic pressure to the engagement elements C-2, C-3; C-2, B-1.
It is effective that the cutoff valves 77, 78 are valves which use the hydraulic pressure to be applied to the engagement elements C-3, B-1; C-2, C-3 to drain the hydraulic pressure to be applied to the other engagement elements B-1, B-3, and the valve is structured such that only the hydraulic pressure to be applied to the engagement elements C-3, B-1; C-2, C-3 from one direction and to be operated when the hydraulic pressure has been applied to the engagement elements C-3, B-1; C-2, C-3.
It is effective that a hydraulic pressure servo for operating each of the engagement elements C-1 through C-3, B-1, B-3 incorporates a cylinder, a piston hermetically accommodated in the cylinder and a return spring disposed opposite to the operation of the piston, the hydraulic pressure level corresponding to the load of the return spring is made to be the same among the engagement elements, and the cutoff valve is operated when the hydraulic pressure applied to at least one engagement element is raised to a level not lower than the hydraulic pressure corresponding to the load of the return spring.
It is effective that the cutoff valve is structured such that the spring force is exerted on the cutoff valve from at least the other direction and also structured such that balance is kept with the applied hydraulic pressure which is applied to the engagement element from at least one direction, and the spring force is a load corresponding to the hydraulic pressure of the return spring of the engagement element.
It is effective that the cutoff valves 75, 76 are applied with the spring force and a line pressure from the other direction, and the valve is shifted to a position at which the hydraulic pressure to be applied to the other engagement element is drained when either of the engagement elements is in an engaged state and the hydraulic pressure to be applied to the other engagement element is raised to a level not lower than the spring force.
It is effective that the valve 75xe2x80x2 is applied with only the line pressure from the other direction. It is effective that the cutoff valves 77, 78 are applied with only the spring force from the other direction.
It is effective that the fifth engagement element B-1 is provided for an engine brake, a sixth engagement element B-2 is disposed in parallel with the fifth engagement element B-1 and in series with a one-way clutch F-1, and the first pattern further incorporates a combination of the fourth engagement element B-3 and the sixth engagement element B-2.
It is effective that the first valve is a valve structured such that the hydraulic pressure to be applied to the sixth engagement element B-2 is applied to the first valve together with the hydraulic pressure to be applied to the second engagement element C-2, the third engagement element C-3 and the fifth engagement element B-1 and to use the hydraulic pressure to be applied to at least one engagement element to drain the first brake, and the sixth engagement element B-2 is always maintained at a state of engagement in the second speed through the sixth speed.
It is effective that pressure regulating means for regulating the hydraulic pressure applied from the hydraulic pressure source is also provided, the hydraulic pressure applied from the pressure regulating means is applied to a hydraulic pressure servo which operates each engagement element, and the valve is disposed between the hydraulic pressure source and the pressure regulating means.
It is effective that the valves 75, 76 are structured such that the hydraulic pressure between the valve and the pressure regulating means is applied to the valve from one direction and as well as structured such that the hydraulic pressure is applied when the valve is at a first position and the hydraulic pressure is drained when the valve is at a second position.
It is effective that the valve is applied with the hydraulic pressure from the hydraulic pressure source from another direction when the valve is at the second position.
The structure of the first aspect of the invention has the valve for preventing interlocking. Therefore, interlocking of two or more engagement elements, the engagement of which must be prevented, when the forward gear ratio has been realized can be prevented. As a result, deterioration in the durability of each engagement element can be prevented.
The structure of the second aspect of the invention has the valve for preventing the combinations which cause interlocking to occur provided for the structure which realizes six speeds in the forward direction by using the combination of passages for inputting the reduced speed and the planetary gear set. Therefore, deterioration in the durability of the frictional engagement element can be prevented.
The structure of the third aspect of the invention is arranged to selectively engage the five engagement elements to each other to realize the six speeds in the forward direction and is formed such that the foregoing six combinations are inhibited to reliably prevent interlocking. As a result, deterioration in the durability of the frictional engagement elements can be prevented.
The structure of the fourth aspect of the invention is provided with the pressure regulating means corresponding to each engagement element to enable a jump in the gear ratio to be performed. Because the valve is operated with the hydraulic pressure applied to a predetermined engagement element, the need to provide a solenoid for controlling the valve can be eliminated. Thus, a compact structure can be realized.
The structure of the fifth aspect of the invention is such that the means for applying the hydraulic pressure to the engagement element when the reverse gear ratio has been realized to achieve both the prevention of interlocking when the forward gear ratio has been realized and the achievement of the reverse gear ratio when reverse movement is performed if the combination causing interlocking when the forward gear ratio has been realized is the combination for realizing the reverse gear ratio.
The structure of the sixth aspect of the invention is such that the hydraulic pressure is applied to each engagement element through the second passage when the reverse gear ratio has been realized so that the reverse gear ratio is reliably set.
The structure of the seventh aspect of the invention enables hydraulic pressure to be applied to the switching valve through the second passage if no hydraulic pressure is applied to the switching valve from the valve owing to the operation of the valve when the reverse gear ratio has been realized. Therefore, the reverse gear ratio can reliably be realized.
The structure of the eighth aspect of the invention has the solenoid which is capable of selectively interrupting the supply of hydraulic pressure to the engagement element when the forward gear ratio has been realized. As a result, common use of the solenoid is permitted.
The structure of the ninth aspect of the invention enables a solenoid to be omitted. Thus, a compact structure can be realized.
The structure of the tenth aspect of the invention enables a switching valve to be omitted. Thus, a compact structure can be realized.
The structure of the eleventh aspect of the invention is such that the valve is disposed at a position at which the hydraulic pressure source and the engagement element are communicated with each other when the reverse gear ratio has been realized. Therefore, the reverse gear ratio can be reliably realized.
The structure of the twelfth aspect of the invention is such that the force realized by the pressure supplied to the third engagement element C-3 and the spring force are brought into balance. When balance is kept with the line pressure, locking of the valve with the line pressure, which is the hydraulic pressure to be used when reverse movement is performed and which is applied from the other direction, requires an individual pressure receiving surface larger than the pressure receiving surface to which the line pressure is applied. Therefore, the manufacturing cost of the valve spool is increased. On the other hand, the foregoing structure is able to eliminate the need for individually manufacturing the valve spool for applying the line pressure which is the hydraulic pressure for use when the reverse movement is performed. Therefore, the manufacturing cost can be reduced.
The structure of the thirteenth aspect of the invention is such that the valve is independently provided for each of the first pattern and the second pattern. Therefore, a more compact structure can be realized without complicating the hydraulic pressure circuit.
The structure of the fourteenth aspect of the invention is such that the first brake is drained. Therefore, only one valve is able to correspond to the three combinations.
Therefore, a compact structure is realized.
The structure of the fifteenth aspect of the invention is such that the first clutch or the second clutch is drained. Thus, only one valve is able to correspond to the two combinations. Therefore, a compact structure is realized.
The structure of the sixteenth aspect of the invention is such that the pressure receiving portions of the valve are formed into a common structure. Thus, the cost of the machining facilities for realizing accuracy of the coaxiality of the valve spool required when one valve corresponds to the two combinations is reduced.
The structure of the seventeenth aspect of the invention is such that an independent valve is provided for each combination. Therefore, the cost of the machining facilities for realizing accuracy of the coaxiality of the valve spool is reduced.
The structure of the eighteenth aspect of the invention is such that the operation of the valve is started only when breakdown of the control valve for controlling either of the engagement elements occurs and, therefore, a supplying state has been realized. Therefore, any unnecessary operation in a normal state can be prevented.
The structure of the nineteenth aspect of the invention is able to eliminate the need for applying the hydraulic pressure to the other engagement element from one direction. Therefore, the manufacturing cost of the valve spool is reduced.
The structure of the twentieth aspect of the invention is such that the hydraulic pressure levels corresponding to the load of the return spring are made to be the same among the plurality of engagement elements. Therefore, a malfunction of the valve can be reliably prevented.
The structure of the twenty-first aspect of the invention enables the valve to be operated with the hydraulic pressure before the engagement element starts transmission of the torque, that is, the hydraulic pressure of the return spring. Therefore, tie-up occurring when interlocking has occurred can be prevented.
The structure of the twenty-second aspect of the invention has the structure that the hydraulic pressure to be applied to the other engagement element is balanced by the spring force as compared with the structure that the hydraulic pressures of at least two engagement elements and the line pressure must be balanced to switch the valves and, therefore, the design becomes too complicated. Therefore, the line pressure is simply required to be balanced with the hydraulic pressure of one engagement element. As a result, the design can be considerably facilitated.
The structure of the twenty-third aspect of the invention does not require any spring and the like. Thus, the number of the elements is reduced.
The structure of the twenty-fourth aspect of the invention is able to eliminate the need for considering the pressure receiving area of the valve spool when balance is kept by using the line pressure because the balance is kept by only the spring. Therefore, the design can be facilitated and a circuit for applying the line pressure is not required. Thus, a compact structure is realized.
The structure of the twenty-fifth aspect of the invention is such that a valve is independently provided for each of the first and second patterns. Therefore, any special circuit is not required and, thus, satisfactory controllability can be realized.
The structure of the twenty-sixth aspect of the invention is such that the second brake which does not concern the torque transmission is always engaged. Therefore, the first valve can be operated to drain the servo pressure of the first brake. As a result, non-operation of the valve owing to no action on the valve in spite of the engaged state of the engagement elements except for the second brake can be prevented.
The structure of the twenty-seventh aspect of the invention is such that the regulated hydraulic pressure is directly applied to the engagement element. In a case where the valve is disposed between the pressure regulating means and the engagement element, the response deteriorates when the engagement element is engaged because the valve disposed in the passage for applying the regulated hydraulic pressure to the engagement element is made to be a resistance when the regulated hydraulic pressure passes through the valve. As a result, the response can be improved.
The structure of the twenty-eighth aspect of the invention is such that when the valve is operated and the second position is realized, the hydraulic pressure applied to correspond to the hydraulic pressure which is applied to the engagement element is drained. Therefore, when a switch to the second position has been performed, undesirable shift to the first position can be prevented.
The structure of the twenty-ninth aspect of the invention is such that the hydraulic pressure is applied to the valve in the same direction as the direction in which the hydraulic pressure is applied to the engagement element. Therefore, an undesirable switch can be reliably prevented.